yams #149216 attribute permissions: have an 'add' permission distinct from 'update' [validation pending]

Currently 'update' tend to be used for add/update permissions, which hurts specific security models.

prioritynormal
typeenhancement
done in0.39.0
load0.500
load left0.000
closed by#1cb0f8cc8bd8 "add" permission for attributes (to distinguish from "update")
patch"add" permission for attributes (to distinguish from "update") [applied]"add" permission for attributes (to distinguish from "update") [folded]